1. Field of the Invention
The present invention relates to an elevator guidance device that actively guides a moving body such as an elevator cage.
2. Description of the Related Art
An elevator comprises a guide rail arranged in an elevator shaft, an elevator cage that is suspended by a wire, and raising/lowering means (unit) that raise/lower the cage by applying tension to the wire. Since the cage is suspended by the wire, it swings due to imbalances of the load weight or movement of the passengers; however, such swinging is suppressed by its being guided on the guide rails and it therefore ascends/descends along the guide rails. For guidance of the cage, conventionally, a guidance device comprising vehicle wheels in contact with the guide rails and a suspension was employed, however, vibration and noise caused by distortions or joints of the guide rail was transmitted through the vehicle wheels to the passengers and so was a factor impairing the comfort of the elevator. In order to solve this problem, various systems (for example, Laid-open Japanese Patent Publication number Sho. 51-116548, and Laid-open Japanese Patent Publication number H. 06-336383 and the like) have been proposed involving mounting an electromagnet on the elevator cage and guiding the cage in non-contacting manner by having the attractive force of the electromagnet act on an iron guide rail. Of these, Japanese Patent application H. 11-192224 discloses an elevator guide device wherein, in magnetic units comprising an electromagnet constituted by arranging the poles of an electromagnet opposite each other with guide rails in between and facing the guide rails through a gap and a permanent magnet arranged so as to share its magnetic path with the electromagnet in the aforesaid space, guidance control is exercised whereby the attractive forces of these magnetic units that act on the guide rails are stabilized while making the exciting current of the electromagnets converge to zero. By means of this technique, an elevator of low cost can be realized in which a comfortable ride can be provided and installation costs such as those of mounting the guide rails are controlled. However, even in such a case, the following problems arise.
Specifically, when elevator cage guidance control is performed whilst making the electromagnet exciting current of the magnetic units converge to zero, the gap lengths between the magnetic units and the guide rails such that external forces acting on the elevator cage and external disturbance torque due to these are as well as the permanent magnet attractive force of the magnetic units are exactly in balance change. That is, when external force acts on the elevator cage, the gap lengths change such as to oppose the application of the external force. Accordingly, if for some reason excessive external force acts on the elevator cage, the cage moves in the opposite direction to the direction of action of the external force, ultimately causing the magnetic units to contact the guide rails. When the magnetic units contact the guide rails, further external force is applied due to reaction from the guide rails, causing further change of the attractive force of the magnetic units in the guidance control device in the opposite direction to this external force, with the result that further change of the gap length is promoted. Thus, once the magnetic unit contacts the guide rail, guidance control acts such that those gap lengths which had become shorter on contact become even shorter and those gap lengths that had become wider become even wider, with the result that ultimately the elevator cage is completely in contact with the guide rail without any possibility of returning once more to a non-contacting condition.
Even in such a case, for example as disclosed in published Japanese Patent Number H. 06-24405, the phenomenon of adhesion of the elevator cage to the guide rail due to external force can be avoided if the guidance control means (unit) is provided with the function of actuating power control means (unit) having the function of making the electromagnet exciting current converge to zero when the gap length is in a prescribed range. Specifically, the zero power function whereby the electromagnet exciting current is made converge to zero by the guidance control device can be disabled by setting the output of the zero power control means (unit) as in the embodiment of this publication such that it is changed over to zero by setting the operating range of the zero power control means (unit) to be just before contact of the electromagnetic units with the guide rails. Since the attractive force of the magnetic units is controlled so as to return to the set gap length in respect of the external force when operation of the zero power control means (unit) is disabled, it becomes possible for the elevator cage to be again restored to the non-contacting condition by change of the gap length, which had changed so as to oppose the external force, in the direction of application of the external force. However, even in this case, action of the guidance control device of the elevator cage is unsatisfactory. In Published Japanese Patent Number H. 06-24405, magnetic levitation control as described above is applied to a levitation type carrier device. With the chief purpose of completely avoiding contact of the magnetic units and the guide rail in order to prevent generation of dust, in a running carrier vehicle, the gap length is rapidly increased by disabling the zero power control means (unit) in order to avoid contact with the guide rail produced by transient external force applied to the carrier vehicle on for example passage of a step in the guide rail. Consequently, if the gap length is increased by disabling of the zero power control, operation of the zero power control means (unit) is recovered in cases where the external force is not transient, for example cases where the rated carrying weight is exceeded. If this happens, the phenomenon of recovery occurs, in which the zero power control is again disabled by decrease of the gap length. However, even in this case, contact of the carrier vehicle with the guide rail is avoided and the objective of preventing generation of dust is achieved. However, in the case of an elevator, priority is given to a comfortable ride rather than to prevention of generation of dust. Thus, if enabling/disabling of the zero power control means (unit) is determined on the basis of the range of the gap length, if an excessive but steady external force is applied to the elevator cage, continuous fluctuation of the gap length occurs as described above, severely impairing comfort.
In order to solve these problems, it is necessary to make the dimensions of the magnetic units large and to set the gap lengths to a small value beforehand at the design stage, so as to maintain balance with external force by means (unit) of a large change of attractive force for even slight variations of gap length in response to external force, by making the variation of attractive force of the permanent magnet with respect to variation of the gap length large. However, with such measures for solution of the problem, the magnetic units become large in size and high precision is required in the installation of the guide rails, leading, as a result, to the problem of increased costs.
Thus, with the conventional elevator guidance device, there was the problem that since enabling/disabling of the zero power control means (unit) was determined by the gap length between the magnetic units and the guide rails, if an external force of a certain level of magnitude was applied to the elevator cage, the comfort of the ride was severely impaired. Furthermore, if, in order to avoid such problems, the magnetic units were increased in size, the device became of large size; on the other hand, if the designed gap length was set to a small value, installation of the guide rails had to be carried out with great precision, in either case, this made the elevator system complicated and/or large in size, and resulted in high costs.
Accordingly, one object of the present invention is to provide a novel elevator guidance device wherein, in addition to improved comfort, simplification and/or size reduction, lower costs and improved reliability of the device can be achieved.
In order to achieve the above object, an elevator guidance device according to the present invention is constructed as follows. Specifically, it comprises: a guide rail installed in the vertical direction; a moveable body capable of being raised and lowered along the guide rail; electromagnets mounted on the moveable body and comprising magnetic poles that face the guide rails with a gap therebetween and which are arranged so that the attractive forces that act on the guide rails at at least two of the magnetic poles of these magnetic poles are in mutually opposite directions; magnetic units comprising a permanent magnet that supplies magnetomotive force needed for guidance of the moveable body and that is arranged so as to share its magnetic path in the gap with the electromagnets; sensors that detect the condition in the gap of the magnetic circuit formed by the electromagnets with the gap and the guide rail; guidance control means (unit) that control the exciting current of the electromagnets in accordance with the output of these sensors and thereby stabilize the magnetic circuits; zero power control means (unit) that stabilize the magnetic circuits in a condition wherein the exciting current of the electromagnets is zero, based on the output of the sensors; and output limiting means (unit) that set a prescribed saturation value for the output of the zero power control means (unit) and if the output of the zero power control means (unit) exceeds the range defined by this saturation value, make this saturation value the output of the zero power control means (unit).
Also, a zero power control means (unit) may be selected that comprises an integrator that integrates deviations of the exciting current from a prescribed value, with a prescribed gain. Furthermore, a zero power control means (unit) may be selected that comprises a state monitoring device that monitors the external force that is applied to the magnetic guidance system from the output value of the sensors and a gain compensator that multiplies by a prescribed gain the inferred value of the external force monitored by this state monitoring device. In addition, a zero power control means (unit) may be selected that comprises at least a first-order delay filter that inputs the output of the sensors. Also, an output limiting means (unit) may be selected that has the function that, if the output value of the zero power control means (unit) is outside the range specified by the prescribed maximum saturation value and minimum saturation value, if the output value of the zero power control means (unit) is larger than the maximum saturation value, outputs the maximum saturation value and if it is smaller outputs the minimum saturation value and if it is within the range outputs the output value of the zero power control means (unit) unchanged.
Furthermore, an output limiting means (unit) may be selected that comprises a Zener diode arranged with the output terminal of the zero power control means (unit) in the forward direction from the output terminal of a constant-voltage source that defines the maximum saturation value.
In addition, an output limiting means (unit) may be selected that comprises a Zener diode arranged with the output terminal of a constant-voltage source that defines the minimum saturation value in the forward direction from the output terminal of the zero power control means (unit).
Also, an output limiting means (unit) may be selected that comprises a first Zener diode arranged with the output terminal of the zero power control means (unit) in the forward direction from the output terminal of a constant-voltage source that defines the maximum saturation value and a second Zener diode arranged with the output terminal of a constant-voltage source that defines the minimum saturation value in the forward direction from the output terminal of the zero power control means (unit).
Furthermore, an output limiting means (unit) may be selected that comprises an operational amplifier whose positive side power source is a fixed voltage source that defines the maximum saturation value and whose negative side power source is a fixed voltage source that defines the minimum saturation value.
According to the present invention, an elevator cage is guided magnetically in non-contacting fashion by means of magnetic units comprising electromagnets, with respect to an iron guide rail arranged in the vertical direction. The magnetic units comprise permanent magnets that share a magnetic path in the gap between the guide rails and the electromagnets. Guidance of the elevator cage is effected by, if the cage swings for some reason, detecting this swing and changing the electromagnet exciting currents in accordance with the swing, so as to cause attractive force of the magnetic units to act on the guide rail. Swinging of the cage changes the magnetic resistance of the magnetic path due to change of the gap length between the guide rails and the magnetic units, and the electromagnet exciting current provokes variation of the magnetomotive force of the magnetic circuits. Consequently, in the cage guidance control, the gap lengths or exciting currents are detected and the electromagnets are excited with a current or voltage calculated from these values. In these circumstances, when the zero power control means (unit) is operating, in the steady condition, the exciting currents of the electromagnets converge to zero and the gap lengths of the magnet units are changed so that the attractive forces produced by the permanent magnets of the plurality of magnet units mounted on the elevator cage are mutually in balance and non-contacting guidance is achieved. When in this condition external force acts on the elevator cage, swinging of the cage is produced, but the electromagnets are excited so as to suppress this swinging. By action of the zero power control means (unit), the gap length between the magnet units and the guide rails is changed by attractive force produced by the excitation of the electromagnets with the result that ultimately the exciting currents converge to zero at a gap length such that the attractive force of the permanent magnets and the external force are in balance, causing the swinging of the elevator cage to be arrested. Consequently, when the external force and the attractive force of the permanent magnets are in balance, the gap length of the magnetic poles that generate attractive force opposing the external force becomes narrower, and contrariwise the gap length of the magnetic poles that generate attractive force in the same direction as the external force is increased. An elevator guidance device using such zero power control is described in detail in Published Japanese Patent No. H. 06-24405, so a detailed description of the operation of the zero power control means (unit) is here omitted.
Once the magnet units come into contact with the guide rails due to application of a large external force when the zero power control means (unit) is operating, the electromagnets are excited in such a way as to increase the degree of contact, so it is impossible for the elevator cage to return again to the non-contacting condition. Consequently, in the present invention, there is provided output limiting means (unit) that limits the output of the zero power control means (unit) in accordance with its own output value. If excessive external force is applied during operation of the zero power control means (unit), the output of the zero power control means (unit) increases, trying to reach a gap length at which a permanent magnet attractive force overcoming this would be obtained. If this happens, when the output of the zero power control means (unit) is saturated, the function of the zero power control means (unit) is disabled at this time point. When the zero power control means (unit) is in operation, the guidance control means (unit) performs guidance control such that the gap length becomes a value obtained by adding the gap length deviation based on the output value of the zero power control means (unit) to the set value of the gap length, which is set to a prescribed value; however, when the output of the zero power control means (unit) saturates due to the output limiting means (unit), a shift takes place to guidance control targeting the gap length at this time point. Consequently, the gap length that had increased (decreased) in response to external force when the zero power control means (unit) was operating is decreased (increased) in response to the external force when operation is disabled. When, under guidance control by the guidance control means (unit), the gap length decreases (increases) in response to the magnitude of the external force, the sensor detects the change of this magnetic circuit and the electromagnet is excited, causing the attractive force of the magnet unit to increase, whilst the gap length diminishes (increases), with the result that convergence of the change of the gap length takes place, with the attractive force of the magnet unit balancing the external force. Then, when the external force is removed, the gap length tries to return to the value which it had when the operation of the zero power control means (unit) was disabled, by the action of the guidance control means (unit); however, since, at this time point, the external force has already been removed, the input to the zero power control means (unit) acts so as to decrease this output, with the result that this output value is now less than the saturation value, and the zero power control means (unit) again shifts to operating condition. When the zero power control means (unit) again returns to its operating condition, zero power control of the elevator cage is again performed making the gap lengths of the magnet units converge to a width at which the attractive forces of the respective permanent magnets are in balance.
In this way, according to the present invention, thanks to the limitation of the output of the zero power control means (unit) based on its own output value, even though the gap length varies in response to external force, the variation of the output value of the zero power control means (unit) in the vicinity of the control value (saturation value) is continuous and smooth, so vibration of the elevator cage produced by actuation/disabling of the zero power control means (unit) can be avoided. As a result, a comfortable ride can always be obtained. Also, even if excessive external force results in disabling of the operation of the zero power control means (unit) and contacting of the magnet units with the guide rails, at this time point, by the guidance control means (unit), the electromagnets are excited in such a way as to prevent contact, so that, when this external force is removed, the elevator cage can be again restored to a non-contacting condition. Consequently, there is no possibility of the magnet units becoming stuck to the guide rail and an elevator guidance device of high reliability can thus be provided. Furthermore, there is no need to make the magnet units of large size or to make the design values of the gap lengths small as counter-measures to deal with application of external force, so the costs of the elevator system can be lowered.